Fluorescent lamps are, of course, widely used. Such lamps are subject to breakage, particularly when used in rough service environments.
Heretofore, protective plastic coatings or plastic sleeves have been used to protect fluorescent lamps, often to take care of the use of such lamps in low temperature environments. A protective sleeve or coating has another advantage in that if the lamp is struck or dropped so that its envelope shatters, then the protective sleeve can act to prevent the imploding and scattering of the broken glass and the internal components of the lamp, such as mercury, from entering into the environment.
In U.S. Pat. No. 4,506,189 to Nolan et al granted Mar. 19, 1985, a polymeric coating is deposited over the length of the envelope and a portion of the lamp end caps, or terminal base, at each end of the envelope to retain the broken glass and hold the end caps attached to the coating and to the glass surrounding the end caps. In this arrangement, the coating is in direct contact with the glass envelope along its length. Thus, any thermal or mechanical stresses which affect the envelope are also present on the coating.
In U.S. Pat. No. 3,673,401, a protective sleeve for a fluorescent lamp is shown in which an expansible sleeve is held at each end of the fluorescent lamp envelope by a retaining ring. The sleeve inner diameter is larger than the envelope outer diameter so that it is spaced a distance from the envelope. This minimizes the transmission of thermal and mechanical stresses between the envelope and sleeve. The sleeve is expansible so that if the lamp envelope ruptures the sleeve will collapse to accomodate the air rushing into the sleeve to compensate for the low pressure in the envelope and then expand back to its normal shape. Also, the components of this assembly are not assembled to form a substantially unitary structure. Therefore, if the envelope breaks, the retaining rings possibly can detach from the envelope and the broken envelope pieces can spill out of the sleeve.